Our goal in this proposal is to identify and understand the cellular components that internalize and transport endocytic cargo from the apical plasma membrane to the lysosomes of intestinal epithelial cells (enterocytes). Many epithelial cell surface receptors, ion channels, and other integral membrane proteins implicated in human disease are specifically localized to the apical membrane. Their steady-state abundance on the apical surface is largely controlled by their relative rates of insertion and removal from the plasma membrane by secretion and endocytosis. To gain new insight into the mechanisms that drive this pathway, we propose to pioneer the use of the microscopic nematode worm C. elegans for these studies. We will take advantage of the unique experimental features of this system, creating a new, highly simplified, and genetically manipulatable paradigm for this research area. Chief among the features that have made C. elegans a leading model organism in nearly all areas of modern biological research are its highly advanced genetics, including extremely facile gene knockdown, knockout, and transgenic technology, coupled with a transparent body that allows visualization of fluorescently tagged molecules in the physiologically relevant context of the intact living organism. Our preliminary studies have already uncovered a novel regulatory pathway controlling apical endocytosis through Rac1/CED-10. Further analysis will dissect the mechanisms by which this pathway controls apical endocytosis. In addition, we plan to apply the unique genetic tools available in C. elegans to identify additional regulators of apical endocytosis conserved with mammals. As the simplest animal model possessing a true intestinal epithelium, C. elegans has the potential to answer key questions regarding the mechanism of apical intestinal function, and can provide a key framework that catalyzes future investigation into the highly related pathways in mammalian intestinal epithelia. PUBLIC HEALTH RELEVANCE. Our goal in this proposal is to identify and understand the cellular components that internalize and transport macromolecules from the apical plasma membrane to the lysosomes of intestinal epithelial cells (enterocytes). Many important proteins implicated in human disease are specifically taken up from the apical membrane by endocytosis, which is specialized in enterocyte cells, and displays important differences from related processes in other types of cells. Thus this research will be relevant to nutrient uptake, fluid homeostasis and dysentery, and fetal antibody transport.